Amplitude shift keying is a form of amplitude modulation that represents digital data as variations in the amplitude of a carrier wave. The simplest and most common form of ASK operates as a switch, using the presence of a carrier wave having a fixed amplitude to indicate a binary one and the absence of the carrier wave to indicate a binary zero.
For battery-less communications, a wake up receiver is necessary to detect signal energy using certain modulation. In ASK, the signal detection generally happens using an automatic gain controller (AGC) to operate with the large dynamic range of the input signal. The input signal itself may be spectrally located in the middle of large blocker tones, and should still be detected and demodulated. To minimize energy consumption, the AGC loop needs to be very fast so that signal is detected within 2-3 system clock cycles.
Present state of the art wake up receivers typically employ costly off-chip components such as Surface Acoustic Wave (SAW) or Bulk Acoustic Wave (BAW) filters to either filter out unwanted signals and/or provide a stable clock for the receiver operation such that a power hungry phase locked loop is necessary. In addition, existing wake up receivers utilize significant duty cycling to reduce power, such that the ON current of such receivers is of little concern. For example, if a receiver consumes 10 milliwatts power for peak performance and is duty cycled 0.01%, the average power consumption becomes 1 microwatt. While this is an attractive scheme for saving power, it does not fulfill the requirement of many systems where ubiquitous monitoring is necessary, e.g., for sensor applications.